The present invention relates to a method and apparatus for scheduling, synchronizing and controlling the operations of a glassware forming system wherein raw materials are thermodynamically converted to glass containers and packaged. The system includes the control of a plurality of multisectioned machines called IS machines. The system also includes a furnace and forehearth for forming molten glass and a lehr for annealing the glass containers. More particularly, this system relates to a computer control system for controlling the formation of molten glass and for thermodynamically converting the molten glass to glassware containers. Techniques for forming molten glass from raw materials are known. They include initially weighing and mixing in proper proportions the raw materials which form glass. In the prior art this was done on a batch basis and the mix was conveyed to a furnace where the mixture was melted and a homogeneous composition of molten glass was thus formed. The molten glass was then fed to one or more forehearths where the molten glass was cooled to the proper temperature for a particular job, i.e., for processing in a glass container forming process. After reaching the appropriate temperature, the molten glass was forced through one or more orifices in a feeder mechanism and was appropriately shaped by the orifice. The charge of glass forced through the orifice was sheared by a gob shear mechanism to form gobs of molten glass. The gobs were then distributed on a sequential basis to each of a plurality of sections of a multi-sectioned glass container forming machine, called an IS machine.
In the individual section glassware forming machine, a plurality of individual glassware forming sections operate on an interdependent timed basis. The operating cycles of the individual sections are phased with one another for the purpose of maximizing the rate of thermodynamic conversion of molten glass to glass containers. Gobs of hot glass are fed to the individual sections of the IS machine in sequence from the feeder. As one of the individual sections is receiving a gob, another individual section is delivering a freshly molded article to a conveyor system. The other individual sections are engaged in various steps which are intermediate between receiving a gob and delivering ware to the conveyor. An example of one such glassware forming machine is disclosed in U.S. Pat. No. 1,911,119, issued to Ingle on May 23, 1933.
The Ingle glassware forming machine was originally controlled by a mechanical timing drum. However, in the recent past, certain electronic control systems associated with glassware forming machines have been developed which are synchronized to the mechanical operations of the machine. For example, in one prior IS machine system, an operator manually adjusted and controlled certain motors in the machine and the electronic control system sensed the position of a component of the machine for deriving speed information. Specifically, speed information was measured by a shaft encoder or similar device to generate a pulse which could be used as a basis for determining the operating stage of the IS machine in the glassware forming cycle. Such a system is disclosed in U.S. Pat. No. 3,762,907, issued to Quinn et al on Oct. 2, 1973. Thus, the control electronics were synchronized to the control motors of the glassware forming machine. The commonly assigned copending application of Wood, Ser. No. 281,565 discloses a programmable timing controller for an IS machine which is not synchronized to a shaft encoder. This Wood invention can be conveniently used in conjunction with the present invention and the disclosure of the Wood application is incorporated herein by reference thereto.
The glass containers formed by the IS machine are conveyed from the IS machine to a lehr where the containers are "stacked" in rows and annealed. At the output of the lehr, the containers are tested for defects and packaged for shipment to customers.
The operating procedures of prior art control systems are unsatisfactory in several respects. For example, there was no way in which one could accurately control the proper rate and amount of molten glass being formed dependent upon the "pull" of the multi-section machines. Further, with companies having glass plants in a number of locations, plant utilization is determined on an independent basis without central coordination so that plant utilization is not as efficient as possible.
With respect to the IS machines, in one IS machine controller, each job change required the operator to manually set the timing of components relating to the production and transfer of the glassware for each individual section. Significant opportunity for human error thus existed during set-up. Furthermore, job changes, include adjustment of the fluid pressure supplied to various operating valves in the valve block. Furthermore, timing changes during operation are time consuming and must be done by an operator in close contact with the mechanical systems of the machine.
Because of the dispersed, as opposed to centralized, control in the prior art of each IS machine, the complexities of job scheduling to achieve the most efficient and cost effective manufacture of the glass containers was aggravated. Job scheduling involves monitoring the availability of raw materials, availability of molds for a given container type, consideration of the ultimate destination of manufactured ware, and the current demand on machine time considering the jobs in progress. Effective job scheduling presently requires close cooperation between all operating personnel and is seriously jeopardized by any operator inattention and/or error.
Accordingly, there is need in the art for an improved control system for controlling the forming of glass containers including the operation of the furnace, forehearth, the IS machines and the lehrs which system will avoid the problems associated with job changes, operating parameter changes during operation and which will facilitate economical use of glassware forming machinery, and provide improved job scheduling in the glass factory.